Examination of the effects of a 30 km/h speed limit on arterial roads in urban areas on traffic flow, traffic safety and air quality


In the political and public debate on improving environmental conditions in cities and municipalities - initially with a focus on noise pollution, but now also with regard to air quality and climate - the introduction of 30 km/h speed limits on arterial roads is being discussed to varying degrees as a measure for reducing traffic-related emissions. The scenarios under discussion range from an extension of the current practice to larger parts of the main road network to a comprehensive maximum speed limit of 30 km/h in the entire inner-city road network. This raises the question of the traffic-related effects of these measures, especially with regard to the capacity of intersections with traffic signals.


Only by taking a comprehensive look at the effects on traffic flow, traffic safety and air quality can the discussion about the consequences of imposing a 30 km/h speed limit on main roads be objectified. It is thereby necessary to consider various scenarios with regard to the scope of a 30 km/h speed limit on arterial roads and to evaluate their effects. Starting from today's practice without or with only a few "selected" sections restricted to 30 km/h (e.g., in Aachen), various extensions of route-related speed limits to 30 km/h - which should not be defined across the board, but rather specifically in each case, depending above all on the network structure - are possible. In addition to 30 km/h, 40 km/h will also be considered. The effects of 30 km/h or 40 km/h on traffic flow, traffic safety and air quality can only be examined on an exemplary basis for selected municipalities, and in some cases only for individual network sections of main roads. However, these results are to be used as a basis for extrapolating the expected effects of a nationwide change in regulation practice on traffic and service quality.


Within the scope of the project, the introduction of 30 or 40 km/h speed limits will first be empirically investigated at intersections and sections of arterial roads in five different municipalities - measurements will be taken before and after the introduction of the reduced speed limit. Based on the findings of the empirical investigations, microscopic traffic flow simulations are calibrated. These serve as the basis for a simulation study in which the empirical findings are extrapolated to a variety of other scenarios. Empirical and simulation results are evaluated with regard to the effects of the reduced speed limit on traffic flow, traffic safety, noise emissions and air quality. Thus, general recommendations and hints for the introduction of a 30 km/h or 40 km/h speed limit will be derived, which shall serve both for the practice and especially for the policy as a scientifically supported decision support in the discussion about the arrangement of a 30 km/h or 40 km/h speed limit and its consequences. In this project, the Institute for Transport Studies is responsible for the microscopic traffic flow simulations of intersections with traffic signals.